Field of the Invention
The present invention relates to an incandescent lamp loaded in, for example, an automobile.
Description of the Related Art
An incandescent lamp is known, as an automobile headlight, which includes: a bulb made of soft glass; a sealing part made of soft glass sealing the bulb; a pair of lead wires which has, in the bulb, standing portions standing from the sealing part in a manner such as to face each other and which penetrates through the sealing part while being firmly fixed thereto to be exposed to an outside of the sealing part; a filament which is arranged between the standing portions of the pair of lead wires and which has both end parts held at tip parts of the respective standing portions; and a bridge made of soft glass which is arranged between the standing portions of the pair of lead wires on a side located closer to the sealing part than the filament and which has both end parts coupled to the respective standing portions.
A Dumet wire is typically used as the lead wire. The Dumet wire has a structure such that a core part formed of an alloy of iron and nickel is coated with copper, and has a close thermal expansion rate to thermal expansion rates of the sealing part and the bridge made of soft glass. Therefore, it is possible to improve sealing performance of a part of the sealing part through which the Dumet wire is penetrating and coupling performance of a part of the bridge through which the Dumet wire is penetrating after the sealing part and the bridge through which the Dumet wire is penetrating are melted, cooled, and solidified at time of production of the incandescent lamp.
The filament is held at tips of the lead wires with the tips being bent downward. A temperature of the filament turns high when the incandescent lamp is turned ON, and as result of repeatedly turning ON and OFF the incandescent lamp, holding parts of the lead wires holding the filament gradually open while subjected to gradual embrittlement and the filament falls off the holding parts, thereby facilitating disconnection of the holding parts.
Japanese Patent Application Laid-open No. 2015-185419 and Japanese Patent Application Laid-open No. 2015-185449 disclose incandescent lamps which address the aforementioned problem. With the incandescent lamps, a lead wire is divided into a filament-side portion and an electrode-side portion, and the electrode-side portion is of a Dumet wire but the filament-side portion is of a wire material, in place of the Dumet wire, which consists primarily of molybdenum with a high melting point.
The incandescent lamp 1 disclosed in Japanese Patent Application Laid-open No. 2015-185449 has the filament-side wire material further formed to be thinner than the electrode-side Dumet wire, so that upon welding coupling between end parts of the wire material consisting primarily of molybdenum and the Dumet wire, the end part of the Dumet wire melts and is coupled to the end part of the wire material consisting primarily of molybdenum in a manner such as to surround the end part of the wire material, thereby improving of the coupling strength between the both.
Incandescent lamps loaded in, for example, automobiles are subject to vibration and impact. The opening of the holding parts of the lead wires holding the filament facilitates separation of the filament and the lead wires from each other when the incandescent lamp is subjected to vibration or impact, facilitating the disconnection. Therefore, there arises a strong demand on the incandescent lamp for reinforced vibration resistance and impact resistance.